docs: small changes to plotly-express readme (#681)

I looked over the additions I made to the readme, and noticed some small
problems. This fixes them.

plugins/plotly-express/docs/README.md

@@ -123,16 +123,16 @@ The documentation for Deephaven Express routinely uses some common terms to help
 
 - **Variable**: Variables, usually represented as columns in a Deephaven table, are a series of data points or observations of a particular characteristic in the data set. Examples include age, GDP, stock price, wind direction, sex, zip code, shoe size, square footage, and height.
 
-The following terms define different types of variable. Variable types are important because any given plot is usually only intended to be used with a specific variable type:
+The following terms define different types of variables. Variable types are important because any given plot is usually only intended to be used with specific variable types:
 
 - **Categorical variable**: This is a variable with a countable (often small) number of possible measurements for which an average cannot be computed. Examples include sex, country, flower species, stock symbol, and last name. Zip code is also a categorical variable, because while it is made of numbers and can technically be averaged, the "average zip code" is not a sensible concept.
 - **Discrete numeric variable** (often abbreviated to _discrete variable_): This is a variable with a countable number of possible measurements for which an average can be computed. These are typically represented with whole numbers. Examples include the number of wins in a season, number of bedrooms in a house, the size of one's immediate family, and the number of letters in a word.
 - **Continuous numberic variable** (often abbreviated to _continuous variable_): This is a variable with a spectrum of possible measurements for which an average can be computed. These are typically represented with decimal or fractional numbers. Examples include height, square footage of a home, length of a flower petal, price of a stock, and the distance between two stars.
 
-The following terms define relationships between variables. They do not describe attributes of a variable, but describe how a variable relates to others:
+The following terms define relationships between variables. They do not describe attributes of a variable, but describe how variables relate to one another:
 
-- **Explanatory variable**: A variable that other variables depend on in some important way. The most common example is time. If explanatory variables are displayed in a plot, they are presented on the x-axis by convention.
-- **Response variable**: A variable that depends directly on another variable (the explanatory variable) in some important way. A rule of thumb is that explanatory variables are used to make predictions about repsonse variables, but not conversely. If response variables are displayed in a plot, they are presented on the y-axis by convention.
+- **Explanatory variable**: A variable that other variables depend on in some important way. A common example is time. If explanatory variables are displayed in a plot, they are presented on the x-axis by convention.
+- **Response variable**: A variable that depends directly on another variable (the explanatory variable) in some important way. A rule of thumb is that explanatory variables are used to make predictions about response variables, but not conversely. If response variables are displayed in a plot, they are presented on the y-axis by convention.
 
 ## Contributing